An electromechanically operated poppet valve in the cylinder head of an internal combustion, as disclosed in U.S. Pat. No. 4,455,543, is actuated by energizing and de-energizing electromagnets acting upon an armature coupled to the poppet valve. Because the actuation of the electromagnets is controlled by an electronic control unit, valve opening and closing events occur independently of engine rotation. In conventional engines with camshaft actuated valves, which have timings based on engine rotation, air delivery to the cylinders is controlled by a throttle valve placed in the inlet duct of the engine. In contrast, electromechanical valves are capable of controlling air delivery based on valve timing, thereby providing a thermal efficiency improvement over throttled operation of a conventional engine.
However, a drawback to electromechanical valves, particularly at low torque, is the undesirable noise generated when the valves impact upon opening and closing. Furthermore, because there is no throttling, or less throttling, the incoming air through the valves has very little turbulence. The ensuing combustion wave propagates very slowly through the relatively quiescent mixture, leading to combustion instability and rough operation. Furthermore, fuel-air mixing, particularly in engines with direct fuel injection, is insufficient at low turbulence levels.